斜生栅藻中虾青素的积累过程及其光合活性变化

THE ACCUMULATION OF ASTAXANTHIN AND THE RESPONSE OF PHOTOSYNTHETIC ACTIVITY IN SCENEDESMUS OBLIQUUS

分析了斜生栅藻(Scenedesmus obliquus)在光温(30℃,180μmol/m2·s)胁迫条件下积累虾青素的过程,观察了该过程中细胞形态及细胞光合生理的变化。胁迫条件下,细胞在48h内生成并积累了包括海胆酮、角黄素、金盏花黄素和金盏花红素在内的多种次生类胡萝卜素,并合成了虾青素及其酯。该过程中,细胞形态由两端尖细变得不规则、膨大,原来由4、8个细胞组成的定形群体变为游离的单个细胞或2个细胞组成的群体。藻细胞光合速率在24h内先下降后上升,而后又呈现下降趋势,从34.29μmolO2/mg Chla/h迅速下降为5.21μmolO2/mg Chla/h;呼吸速率在前24h内升高至60.37μmolO2/mg Chla/h,而后缓慢下降到38.40μmolO2/mg Chla/h;光合系统Ⅱ的活性随着胁迫时间的延续而逐步下降,较初始值降低了63.9%。结果表明,斜生栅藻细胞在高光照条件下可以合成虾青素,并通过调节光合速率、呼吸速率以及光合系统Ⅱ的效率来应对胁迫。

The accumulation of astaxanthin in Scenedesmus obliquus under stress conditions was analyzed, and the responses of photosynthetic activity and morphological change of algal cells were observed in the study. Under the temperature of 30℃ and illumination of 180 μmol/m^2·s, the content of chlorophyll fell to 4.20 mg/L from initial 5.59 mg/L while the content of carotenoid rose up from 0.25 mg/L to 0.44 mg/L in 48 hours. The composition of individual carotenoid was isolated and identified by HPLC/MS analysis. The results showed cells accumulated secondary carotenoids such as echinenone, adonixanthin, canthaxanthin, adonirubin and 3＇-hydroxyechinenone and so on, the ketocarotenoid astaxanthin （3,3＇ -dihydroxy-β, β-carotene-4,4＇-dione） was found as a final product for the synthesis of secondary carotenoid. With the accumulation of secondary carotenoids, the algal coenobium composed of 4 or 8 cells was split up into single or two cells, and the shape of cells changed into swollen and irregular contrast to their initial state. The photosynthetic activity was also influenced by the stress conditions. The photosynthetic rate decreased about 50% in the first 3 hours, and then went up from 19.54μmol O2/mg Chlα/h to 34.29 μmol O2/mg Chlα/h in the next 9 hours. From 12 hours to 48 hours, the photosynthetic rate experienced a dramatically drop and reduced to nearly 5.21 μmol O2/mg Chlα/h. The respiration rate of algal cells showed an inverse trend, which increased from 18.24 μmol O2/mg Chlα/h to 60.37 μmol O2/mg Chlα/h in the first 24 hours although there was a fluctuation in this course, then it decreased to 38.40 μmol O2/mg Chlα/h in the next 24 hours which was still more higher than that of the control group. The change of chlorophyll fluorescence tended to be similar to that of photosynthetic rate and decreased by 63.9%. These results indicated that the S. obliquus cells could biosynthesize astaxanthin by induced conditions. The accumulation of secondary carotenoids led the changes of contents ratio for chlorophyll to carotenoid. The light inhibition, enhanced respiration rate and the damage to PS Ⅱ were all responses to the stress, which also yielded more metabolism products and reactive oxygen species which further engendered the biosynthesis of secondary carotenoids. Simultaneously, stress conditions inhibited the cell division and led the changes of cell morphology. The regulating of photosynthetic activity and carotenoids accumulation were both the phsioligical mechanism for algal cells to resist the inclement environmental conditions.